Process of making superphosphate.



H. WILLIAMS.

rnocass OF MAKING SUPERPHOSPHATE.

L 1 9 1 0w 1 I p e S d e l n e t a P am 0 9 1 9 2 Y L U Tu D E L I F N o I T A U I L P P A snwnlioz Rinaldo Williams Witnum MM Mail STATES PATENT OFFICE.

RINALDO WILLIAMS, F BIRMINGHAM, ALABAMA.

PROCESS OF MAKING SUPERPHOSPHATE.

Specification of Letters Patent.

Patented Sept. 19, 1911.

Application filed July 29, 1908. Serial ltd 445,885.

ing is a specification.

My invention relates to an improved process for the manufacture of superphosphate or acid phosphate, particularly where phosphate rock containin a relatively large percentage of impuritles, such as oxid of iron, alumina, etc., is treated with'sulfuric acid to form available phosphoric acid in the form of CaO2I-I,OP O,, or

According to old practice the crushed phosphate rock and an approximately equal quantity by weight of sulfuric acid are introduced into a pan where the usual reaction takes place, the mixture and the pan both becoming highly heated to 212 Far. and over.. In this practice, there is added to the ground rock, an amount of acid con siderably in excess of that required to convert simply the insoluble phosphate of lime or tri-calcic phosphate into the soluble or available phosphoric acid, or soluble phosphate of lime, this excess being made nec essary by the combination of a certain proportion of the acid with the impurities in the rock. As these impurities will not be converted into available phosphoric acid,

they remain a neutral element in the resultant acid phosphate which lowers its percentage of available phosphoric acid and increases its transportation charges per unit of available phosphoric acid which constitutes the basis of sale. 7.

Obviously, 'a considerable advantage will be gained if the action of the sulfurlc acid on the impurities in the hosphate rock can be avoided, as less sul uric acid will'be added to the mixture, thereby giving a higher percenta e of phosphoric acid per unit of weight 1n the resulting acid phoshate. p I have found that sulfuric acid will not act on the impurities in the phosphate rock, or at the most will act but little where the reaction between the acid and phosphate takes place at a low temperature. In other words, when the sulfuric acid and crushed phosphate rock are mixed in the pan or retort if the mixture and, if necessary, the

pan itself be kept cool or below 100 F., the sulfuric acid will act onlyon the tricalcic phosphate in the rock, converting the latter almost entirely into available phosphoric acid in an acid phosphate mixture which will contain in addition to said acid phosphate only the quantity of impurities originally in the phosphate rock, the same constituting practically a fixed element.

Referring to the accompanying sheet of drawing in which I illustrate one form of apparatus adapted for carrying out my improved process, the phosphate rock 1, preferably ground to dust which will pass through from to 200 mesh screen, is fed downwardly from the hopper 2 through a spout 3 into the mixing pan 4. The sulfuric acid enters the an through a pipe 5 which has interposed in it a coil 6 disposed in a brine tank 7, the upper end of the pipe 5 extending beyond the tank 7 and being supplied with sulfuric acid in any suitable manner, Brine is introduced in the tank 7 through an opening 8 and is maintained at a low or refrigerating temperature by an ammonia coil 9, which leads downwardly from the tank 7 and continues as a coil 10 disposed in a brine tank 11 which surrounds the pan 4. I prefer to maintain the temperature as low as 100 F. and I consider that the benefits of my process will be increased to an extent as the temperature is lowered further as much as is commercially practicable. This tank is preferably formed as a space between the inner and outer walls of the pan and has a port 12 for the supply of brine, the pipe 9 passing out from the tank 11 and continuing to any suitable refrigerating apparatus. The ammonia coil W1ll act upon the brine in the tanks 7 and 11 to refrigerate the sulfuric acid before it enters the pan and also to chill or refrigerate the mixture in the pan, thereby maintaining the mixture at a low temperature as above indicated, for ,the purposes and with the benefits herein described.

According to the old practice, the quantity of impurities in the rock is practically twice as much in the resulting mixture, as in raw phosphate rock, due to the above described action of the sulfuric acid 011 the impurities in the rock. For example, in tests which I have conducted where 1000 lbs. of phosphate rock were mixed with 1100 lbs. of sulfuric acid of 50 Baum and treated according to the old process, the resulting acid phosthe tests which I conducted according to my improved process, the temperature of the reacting mixture was artificially lowered to about 100 Far. The extent to which the temperature should be artificially lowered, according to my process, varies with the different conditions of practice and I do not therefore limit myself to any definite degree of lowering, provided the same constitutes a substantial lowering of the temperature below that normally reached by a reacting mixture according to present practice. A similar quantity of the same rock treated by my process at a tem erature of about 100 F. and to which on y 900 lbs. of sulfuric acid of 50 Baum were added, gave 17.23% available phosphoric acid in the resultin acid phosphate. I find from a number of tests that, where a low grade phosphate rock containing a relatively high percentage of oxid of iron and alumina is treated by the old process, the conversion of the tricalcic phosphate in the rock is not complete,

frequently leaving as high as 2 and 3%' of phosphoric acid in insoluble form in the resultant mixture, whereas when the treatment is in accordance with my process, this loss is practically eliminated, the insoluble phosphoric acid being almost entirely converted into available phosphoric acid, the

percentage of insoluble phosphoric acid remaining, being less than one-half of one per cent.

From the foregoing it will be seen that my process gives marked economy both in the quantityof sulfuric acid required for treating a given quantity of phosphate rock and also in the higher percentage of available phosphoric acid per unit of resulting acid phosphate.

The mixture mav be kept cool and at the desired low temperature during reaction in any suitable manner, such as by cooling the pan with a forced circulation of air, water,

or, as illustrated, with a refrigerating fluid, and by similar means the sulfuric acid and the phosphate rock, either or both, may be as low as 32 F. if desired chilled before introduction into the pan. By artificially lowering the temperature of the reacting mixture, I mean to cover any means for perature which is materially lower than it would be but for such artificial treatment, and this may" be accomplished as above stated by the use of a cooling medium artificially applied to the mixture or by chilling its component elements.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is I 1. The improved process for the manufacture of superphosphate which consists in treating ground phosphate rock with sulfuric acid in the customary manner to form a wet mixture, and artificially lowering the temperature of the reacting mixture of acid and phosphate rock.

2. The improved process for the manufacture of superphosphate which consists in addin to the phosphate rock only sufficient sulfuric acid to convert the tri-calcic phosphate therein into soluble phosphate of lime and artificially lowering the temperature of the reacting mixture of acid and phosphate rock, substantially as described.-

RINALDO WILLIAMS.

Witnesses NoMrE WELSH, ANNE; L. PEACE.

causing the reaction to take place at atem- 3. The improved process for the manu- 

